This simple-as-it-gets lentil soup has a million variations. Stir in some cooked bulgur and a sprinkle of parmesan before serving. Or sauté a little curry powder with the onion. Or toss in baby spinach or kale for the last minute or two. Or add minced fresh herbs or pesto just before eating. For a creamy soup, purée 1 or 2 cups, then stir them back into the pot.