Beat eggs with 1/4 teaspoon salt. Heat oil in a 10-inch heavy nonstick skillet over medium-high heat until it shimmers, then sauté cauliflower until browned and tender, 5 to 9 minutes. Reduce heat to medium, then add garlic, 1/4 teaspoon salt, and 1/8 teaspoon pepper and sauté 1 minute. Pour eggs over cauliflower. Cook, lifting edges to let uncooked egg run underneath and shaking skillet occasionally to loosen omelet, until almost set, 4 to 5 minutes. Slide out onto a large plate. Put skillet over omelet and, using pot holders, firmly hold plate and skillet together, then invert omelet back into skillet and cook 1 to 2 minutes. Slide out onto plate and sprinkle with feta and parsley.