Preheat the oven to 400 degrees F. If you aren't using store-bought tostada shells, make your own by following the directions below.
Toss the corn kernels, zucchini, bell pepper, and tomato with olive oil and seasonings, ensuring all the vegetables are well-covered with the seasonings. Place in a single layer on a baking sheet and roast for 25 minutes, tossing halfway through.
Open the can of beans and warm either on the microwave or stove.
While the vegetables are cooking, top the tostada shells with the refried beans. Place the tostadas on a separate baking sheet and sprinkle with the shredded cheese. Place in the oven and cook for 2-3 minutes until the beans are hot and the cheese is melted.
Top the tostadas with the roasted vegetables and any other toppings you'd like.
Notes
To make your own tostadas: You'll need corn tortillas and cooking spray. Preheat your oven to 400 degrees F. Spray a baking sheet (or two) with cooking spray and both sides of your corn tortillas. Place in a single layer on a prepared baking sheet and lightly season with salt. Bake for 5 minutes, then flip and bake another 5-8 minutes until crispy and chip-like. Now you are ready to top your tostadas!