Saute garlic and onion with olive oil in heavy-bottomed pot. Add lentils and stir for one minute. Cover lentils (one-inch over) with broth and bring to boil. Reduce heat to simmer and cook lentils until done. Add spinach, tossing until wilted. Add feta and squeeze lemon juice over.
Serve warm or at room-temperature plain, or over brown or white rice.