Heat olive oil over medium heat in an oven-safe skillet. Add the potato slices and onion. Fry, stirring occasionally, over medium heat for about 5 minutes. Add garlic and cook until potatoes are tender but not browned (20-25 minutes). Set aside.
Whisk the eggs and combine the cooked potatoes with the eggs and stir. Spread the egg-coated potatoes into the remaining oil in the skillet. Heat on medium-low and cook, shaking the pan frequently and/or stir frequently being careful not to break potatoes, until mixture begins to set (about 12 minutes).
While the tortilla is cooking, make the red pepper sauce by adding all ingredients to a food processor or strong blender and blend until smooth.
Place the pan in the oven and broil on low for 6 minutes.
Remove and cover the skillet with a plate, and using oven mitts, carefully invert the omelette onto the plate. Allow to cool then cut it into 8 even wedges. Season with salt, if needed, and roasted red pepper sauce.