Prepare and Roast the Vegetables: Preheat your oven to 400ºF (200ºC). Arrange the sliced onion, chopped bell peppers, mushrooms, and corn kernels in a single layer on one or two large baking sheets. Drizzle with 1 tablespoon of olive oil, then season generously with salt and freshly ground black pepper. Toss the vegetables to coat evenly with the oil and seasoning. Place the trays in the oven and roast for about 30 minutes, stirring two or three times during cooking, until the vegetables develop a golden-brown caramelized color and become tender.
Crisp the Tortillas: While the vegetables roast, prepare the corn tortillas. Lay them out in a single layer on a clean baking sheet (do this in batches if needed). Lightly brush or spray both sides of each tortilla with olive oil. Place the tortillas in the oven and bake for 10 to 15 minutes, flipping halfway through, until they are crispy and just starting to brown. Keep a close eye to avoid burning.
Combine Vegetables and Beans: Once the roasted veggies are done, transfer them to a large mixing bowl. Add the rinsed and drained black beans to the bowl and gently fold everything together. Taste and adjust salt and pepper as needed to enhance the flavors.
Assemble the Tostadas: Remove the crispy tortillas from the oven and place them on serving plates. Spoon generous portions of the vegetable and bean mixture evenly over each tortilla. If you like, sprinkle shredded Monterey Jack cheese on top while the tostadas are still warm to allow it to melt slightly.
Add Toppings and Serve: Garnish with diced avocado, fresh tomatoes, microgreens, and chopped cilantro if desired. Finish with a squeeze of fresh lime juice and a drizzle of poblano cream sauce or your preferred sauce for extra creaminess and zing. Serve immediately and enjoy!
