Pierce the potatoes with a fork, and arrange in a circle on paper towels in microwave oven. Microwave at high for 16 minutes or until done, rearranging potatoes after 8 minutes. Let stand 5 minutes.
While the potatoes cook, heat oil in a large nonstick skillet over medium-high heat. Add onion, bell pepper, and garlic; stir-fry 5 minutes. Add pizza sauce, pepperoni, and red pepper; reduce heat, and simmer 3 minutes. Stir in tomato and water; simmer 3 minutes.
Split potatoes open with fork; fluff pulp. Spoon pepperoni mixture evenly over potatoes. Top with cheese.