Combine lentils, 3 cups water, 1/2 teaspoon salt and 2 peeled cloves garlic in a small pot. Cover, bring to boil over high heat. Reduce heat, simmer 20 minutes until tender.

Meanwhile, dice onion and carrot, mince remaining 2 cloves garlic, clean and slice mushrooms.

Heat olive oil in a large skillet over medium-high heat. Add onion and carrot, fry several minutes until soft and beginning to brown. Add mushrooms, sprinkle with 1/2 teaspoon salt. Cover. Let cook undisturbed for 5 minutes. Stir. Cover and cook a few more minutes until mushrooms are very brown.

Deglaze with sherry, stirring to scrape the caramelized bits up. Add garlic, oregano, tomatoes, red pepper flakes. Cover, reduce heat to low and simmer until lentils are cooked.

Once lentils are cooked, drain and add to sauce. The whole garlic cloves will be soft and easy to mash into the sauce now. Let simmer, covered, while you boil spaghetti noodles. Add 1/2 cup pasta cooking water to your sauce before draining the pasta (if serving with pasta).