Greek Pasta Sauce

2 tablespoons olive oil
2 cups chopped onions
2 cloves garlic, minced
2 small bunches fresh spinach, washed well,
    large stems removed, and coarsely chopped
1/2 cup sliced pitted black olives (preferably Greek olives,
   such as kalamata)
Juice of 1 lemon
1/2 pound feta cheese, crumbled
Pepper to taste
1 pound cooked penne or other short thick pasta

Heat olive oil in large skillet and cook onions and garlic over medium heat until translucent. Lower heat and add spinach and cook, covered, until wilted, but still green. Add chopped olives, crumbled feta cheese, pepper and lemon juice. Stir in cooked pasta and serve.