In an olla de hierra or heavy bottom pot add the olive oil, onion and whole chorizo. Cook over medium-low heat, turning chorizo occasionally, until onions soften and chorizo starts to brown, about 10 minutes. Remove chorizo, slice and return to pot.
Rinse lentils. Add stock (or water), lentils, whole garlic cloves, paprika, tomato, carrots and potatoes to the pot with the onion and chorizo. Bring to a boil, then lower to a simmer. Let cook uncovered 45 minutes, stirring occasionally. Season to taste with salt and pepper.
Remove the cloves of garlic, squeeze garlic from its skin and mash. Return garlic pulp to the pot.
Serve stew with a crisp green salad, crusty bread and a Spanish Tempranillo wine.