Refried Bean Tostadas

Ingredients

• 6 flour tortillas (8 inches)
• 1/2 pound sliced fresh mushrooms
• 1 cup diced zucchini
• 2 tablespoons canola oil
• 1 jar (16 ounces) chunky salsa
• 1 can (7 ounces) white or shoepeg corn, drained
• 1 can (16 ounces) vegetarian refried beans, warmed
• 1-1/2 cups shredded lettuce
• 1-1/2 cups shredded cheddar cheese
• 2 medium ripe avocados, peeled and sliced
• 1-1/2 cups chopped tomatoes
• 6 tablespoons sour cream