Preheat oven to 400°. Sauté mushrooms in 2 tablespoons olive oil over medium-high heat 2 to 3 minutes or until soft and light brown; set aside.
Heat remaining oil in a paella pan or 12-inch ovenproof skillet, and sauté garlic, onion, and peppers 8 minutes or until soft. Add rice, saffron, and salt, and stir until rice is coated with oil. Add broth, and bring mixture to a boil.
Cover pan with aluminum foil, and bake at 400° for 8 minutes. Stir in reserved mushrooms, artichoke hearts, and next 3 ingredients; cover and bake 8 minutes more. Remove foil, and bake 8 to 12 minutes more or until heated through. Remove from oven, and top with olives, green onions, roasted pepper, and lemon wedges.