
Heat oven to 450° F. Place tortillas on baking sheets and spray with vegetable oil spray. Bake until lightly browned and crisp, about 10 minutes, rotating baking sheets midway through. Place all the tostadas on one baking sheet, set aside but leave the oven on.
In a large bowl, toss together chopped onion, red bell pepper, and zucchini with 2 tablespoons of vegetable oil and ½ teaspoon salt. Place on the emptied baking sheet and roast in the oven until vegetables are tender, about 10 minutes, stirring once or twice.
Combine slaw ingredients in a separate bowl.
Stir together the sour cream and lime juice.
Heat Isadora Beans in a small saucepan. To assemble, on each tostada spread about 2 tablespoons of beans and top with roasted vegetables. Add crumbled queso fresco and slaw. Drizzle with sour cream mixture.