How can I improve the baking of frozen cod and rice with carrots,? This is a dish that I'm trying to figure out. Out of laziness I want to cook a whole meal that includes some veggies, protein and carbs in a single baking.
I don't thaw the cod before because it's usually a dish that I make with no preparation.

I mix diced carrots and rice with oil, salt, pepper, and some spices like rosemary, sage and thyme. Then put the mixture in an over tray add the frozen cod and enough stock for the rice to cook in.
Finally it goes in the oven at ~180*C (~370*F) until the rice is done. 

The result is reasonably good, with flavors from the fish and the carrots blending into the rice, but overall a bit underwhelming.

Any suggestions on what could be improved? Is there some other all-in-one-tray baking recipe I could use?

I'd like to stay away from garlic or onions, but maybe there are other herbs or spices that would work better with the stock and rice rather than the ones I'm using?
I guess I'm wondering which spices are at their best when cooked in lots of water and go well with fish.

The carrots cook well, but they don't really brown, some on top just dry up and others are close to boiled, would lowering the cooking temperature help?

Other vegetables that would work better here instead?
You're not going to get any browning on the vegetables.  By cooking everything together, you're steaming everything, preventing anything from browning.

If the carrots were on the top layer, you could put it under the broiler (top heat)for a minute or two, after everything's cooked through ... but for that, I would put the rice on the bottom, the carrots above them, then the cod.  Cook to your normal doneness, remove the cod and broil until you get some brown on the top.

You might still get away with it if the rice and carrots are mixed together -- there's a special name for the layer of crunchy rice that you get when cooking paella which adds flavor and a contrasting texture.

As for flavorings -- garlic and onion would have been my go-to in this sort of thing ... but I'd also add bell peppers, possibly roasted in advance.  For spices, I'd serve it with za'atar blend -- the citrusy quality of the sumac helps to brighten up dishes.

If you don't have za'atar (most people don't), you could squeeze over a bit of lemon juice, or sprinkle some vinegar over it (but something that tastes good on its own -- apple, wine, etc ... not white).  Tomatoes can also help -- but if it's out of season or you only have grocery store tomatoes available, go with canned tomatoes.  (canned diced are the easiest for this sort of thing)

Another option is to finish the dish with some fresh herbs -- flat leaf parsley, basil, oregano, thyme or culantro might go well with those flavors.

As for recipes -- I'd look at paella recipes -- although it's often cooked with only bottom heat (on a grill or other burner), if you have a suitable shallow pan, you can start it on the stovetop (to brown the carrots a bit before adding liquid), finish assembling, then put it in the oven to finish.