Heat oven to 400°F. Grease four 10-oz. ramekins. Heat oil in medium saucepan on medium-high. Add onion and sauté until tender, about 5 min. Add spinach and sauté until just wilted, about 2 min. Remove from heat.
Meanwhile, in medium bowl, stir together tomatoes, cumin, paprika, 1 tsp. each salt and pepper, and hot sauce, if using. Add onion-spinach mixture and mix to combine. Divide among ramekins.
Crack 1 egg into center of each ramekin, then sprinkle on feta. Bake until whites are set but yolks are still runny, 12 to 15 min.
