Preparation Heat 1/4 cup oil in large ovenproof skillet over medium heat. Add potatoes; simmer in oil 3 minutes. Add onion; sauté until potatoes and onion are almost soft, about 5 minutes. Add mushrooms; sauté until vegetables are soft, about 7 minutes. Add red peppers; sauté 4 minutes. Using slotted spoon, transfer vegetables to large bowl. Cool slightly. Wipe out skillet. Preheat broiler. Stir eggs, 1/2 teaspoon salt, and 1/4 teaspoon pepper into vegetables. Heat 1/4 cup oil in same skillet over medium-high heat. Add egg mixture; cook without stirring until just beginning to brown on bottom, about 3 minutes. Cover skillet; cook until eggs are cooked through, about 3 minutes. Uncover and broil until top is brown, about 3 minutes. Slide spatula around edges and under tortilla to loosen. Slide tortilla onto large plate. Serve warm or at room temperature.
Preparation Heat 1/4 cup oil in large ovenproof skillet over medium heat. Add potatoes; simmer in oil 3 minutes. Add onion; sauté until potatoes and onion are almost soft, about 5 minutes. Add mushrooms; sauté until vegetables are soft, about 7 minutes. Add red peppers; sauté 4 minutes. Using slotted spoon, transfer vegetables to large bowl. Cool slightly. Wipe out skillet. Preheat broiler. Stir eggs, 1/2 teaspoon salt, and 1/4 teaspoon pepper into vegetables. Heat 1/4 cup oil in same skillet over medium-high heat. Add egg mixture; cook without stirring until just beginning to brown on bottom, about 3 minutes. Cover skillet; cook until eggs are cooked through, about 3 minutes. Uncover and broil until top is brown, about 3 minutes. Slide spatula around edges and under tortilla to loosen. Slide tortilla onto large plate. Serve warm or at room temperature.