Roast in oven on a baking sheet for 15 minutes, tossing once halfway through.
While the asparagus roasts, cook lentils by adding them to a medium saucepan and covering with water about 3 inches above the lentils. Bring water to a boil and reduce heat and simmer for 20 minutes.
Once cooked, stir salt, pepper, cumin and red wine vinegar into lentils.
To finish, in a medium bowl, combine spinach, asparagus, lentils, and feta cheese. Dress with your favorite homemade salad dressing.
