Curried Beef and Red Lentil Stew

Name: Curried Beef and Red Lentil Stew
Ingredients: 1 cup red lentils; 2 pounds beef chuck roast cut into 3/4-inch cubes; Kosher salt; Black pepper; 3 tablespoons canola or vegetable oil; 1 medium onion, chopped; 1 tablespoon minced ginger; 2 cloves garlic, minced; 1 tablespoon curry powder; 1 teaspoon ground cumin; 1 bay leaf; 1 14-oz. can diced tomatoes; 2 1/2 cups beef stock; 2 cups loosely packed baby spinach leaves; 1 tablespoon red wine vinegar; 3 tablespoons chopped cilantro; 1/2 cup plain Greek yogurt (optional)