Preheat the oven to 375 degrees F (190 degrees C). Lightly grease a 9x13 inch baking dish.
Combine cooked rice, thawed vegetables, and Cheddar cheese in a large bowl.
Melt butter in a small saucepan over low heat; stir in lemon juice, bouillon granules, paprika, and black pepper.
Add ½ butter mixture to rice mixture; stir to combine. Transfer rice mixture to the prepared baking dish. Place tilapia fillets in a single layer on top of rice; pour remaining butter mixture over top.
Bake in the preheated oven until fish flakes easily with a fork, 35 to 40 minutes.
Tilapia All-in-One Casserole · Dinner Match Lab | Dinner Match Lab