Put beans in 3-quart saucepan and cover with water. Add onion. Bring to boil, then reduce heat and simmer until beans are tender, about 1 1/2 hours. Add additional water, if necessary. Cool beans to room temperature. Drain beans and puree in food processor. Add lemon juice, tahineh, cumin, garlic, salt and cayenne pepper, and puree until smooth. Toast bread slices. Spread scant tablespoon hummus onto each. Spoon about 1 tablespoon peas onto each of 12 toasts and press peas lightly into hummus. Spoon about 1 tablespoon carrots onto each of 12 more toasts and press into hummus. Finish by spooning about 1 tablespoon corn onto each of remaining toasts and pressing into hummus. This recipe yields 36 servings. Each serving: 76 calories; 120 mg sodium; 0 cholesterol; 1 gram fat; 14 grams carbohydrates; 3 grams protein; 0.97 gram fiber.