Heat 2 tablespoons oil in a large nonstick (or well-seasoned cast iron) skillet over medium-high heat.
Add garlic and onions, and cook about 2 minutes.
Add potatoes, salt and pepper, stir well, cover and cook, stirring occasionally, until potatoes are just tender, about 15 minutes.
Transfer to a large bowl
Add spinach and toss well.
Let cool 10 minutes.
Wipe skillet clean.
Stir peppers and eggs into potato mixture.
Heat another 1/2 tablespoon oil over medium heat.
Transfer mixture to skillet and cook, running spatula around edges and gently shaking occasionally to prevent sticking, until eggs are set and bottom is brown, 12 to 14 minutes.
Carefully invert onto a large plate.
Heat remaining oil in skillet and slide tortilla back in, cooked side up.
Cook about 5 minutes to golden brown.
Transfer back to plate and let cool at least 10 minutes.
Slice into wedges and serve.
Serving Size Serves 6
* Percent Daily Values are based on a 2,000 calorie diet. Your daily value may be higher or lower depending on your calorie needs.