Heat a non-stick skillet over medium heat. Warm tortilla on for 1 minute on each side. Remove to a plate.
Heat olive oil in the skillet with a pinch of crushed red pepper. Add onion and garlic and sautée for 2 minutes to soften. Add the stems of the chard and sautée for 2 minutes before stirring in the leaves of the chard. Cook until just wilted and season to taste with salt and pepper. Pile into warmed tortilla (or store in a container to enjoy later).
In a small bowl, beat the eggs with a pinch of each salt and pepper. Return pan to medium-low heat with a bit of olive oil or butter if the pan is dry. Pour in eggs and stir and fold constantly with a rubber spatula or wooden spoon until cooked to desired hardness. Add eggs to tortilla and top with crumbled feta. Enjoy while warm.