Mixed vegetable casserole bakes colorful vegetables in a creamy sauce with a crunchy topping for a vegetarian family side. This healthy, comforting dish is a holiday table staple that makes eating vegetables delicious.
Preheat oven to 375°F and butter a 2-quart casserole dish to prevent sticking.
Steam broccoli, carrots, cauliflower, and green beans together for 5–6 minutes until just tender but still vibrant. Immediately drain to halt cooking.
In a large bowl, combine steamed vegetables, peas, mushrooms, and shredded cheddar. Toss lightly to blend.
Mix cream of mushroom soup, milk, salt, black pepper, garlic powder, and thyme until smooth; pour over vegetables and stir gently for even coating.
Transfer the mixture to the prepared casserole. Melt butter and toss with breadcrumbs; sprinkle evenly on top for a crunchy finish.
Bake uncovered for 25–30 minutes, until topping is golden brown and filling bubbles around the edges. Let cool for 5 minutes before serving for best texture.