Process sesame seeds in the bowl of food processor. Add chick peas or garbanzo beans, 1/4 cup olive oil, garlic, lemon juice, 1/2 tub Knorr® Homestyle Stock - Vegetable and water. Continue processing until smooth. Remove from processor; set aside.
Combine remaining 1/2 tub Knorr® Homestyle Stock - Vegetable with remaining 2 tablespoons water and 1 tablespoon olive oil. Brush onto mushrooms. Grill or broil mushrooms, turning once, until tender, about 15 minutes; slice.
To assemble, spread 3 tablespoons hummus on the inside of each pita bread, then evenly stuff with lettuce, tomatoes and mushrooms. Add additional hummus, if desired.