Serve this pizza with taco fixings such as sour cream, shredded lettuce, chopped tomatoes, and salsa. Choose a jarred prepared salsa on the pizza itself; fresh salsa from the refrigerated case can lead to a soggy crust.
1. Brush grill grate well with oil, and preheat grill to medium.
2. Brush mushrooms and corn with 1 Tbs. oil. Grill 4 to 5 minutes, or until pronounced grill marks form, turning occasionally. Cool until easy to handle. Thinly slice mushrooms, and cut kernels off corncob.
3. Spread beans over crust. Top with cheeses, salsa, mushrooms, corn, avocado, and green onions. Season with salt and pepper, if desired.
4. Place pizza on grill, close lid, and cook 7 minutes, or until bottom of crust is crisp and has pronounced grill marks. Garnish with cilantro, if using.