Heat oven to 350° with a rack in the center position.
Toss together the zucchini, squash, garlic, and 2 tbsp. olive oil on a rimmed baking sheet. Season with salt and pepper and spread the ingredients evenly, leaving space for the fish. Place the fish on the pan and season with salt and pepper.
In a small bowl, combine the panko, Parmesan, parsley, remaining olive oil, and a pinch of salt. Press the mixture onto the fish, distributing it evenly.
Bake until the fish flakes apart when gently prodded with a paring knife, about 20 minutes.