What to do if you don't have a slow cooker: I would assume that you could just cook the lentils on the stove top in the sauce instead of on a slow cooker. Saute vegetables with a small amount of olive oil, then add in the remaining ingredients, bring to a boil, cover, reduce heat to medium and simmer until lentils are tender -- about 35-45 minutes. Uncover and cook longer if more liquid needs to be absorbed.
To cook spaghetti squash: Cut in half, scoop out seeds, and place on a large baking sheet lined with parchment paper. Bake at 375 degrees F for 45 minutes to 1 hour.