In a medium saucepan or pot, bring lentils and water to a boil. Reduce to a simmer, and let lentils cook for 18-20 minutes, just until lentils are tender. Drain water and set the lentils aside.
While the lentils are cooking, slice the cauliflower in half, removing the thick center core. Cut into large chunks.
Using a food processor, break up the cauliflower into small pieces. Pulse the cauliflower until it looks crumbly. Put cauliflower in a bowl. If you don’t have a food processor, you can finely chop the cauliflower into pieces.
In a large heavy-bottomed pot, heat the olive oil over medium heat. Add the onion, red pepper, celery, carrot and cook until soft, about 5 minutes.
Add the garlic and cauliflower to the pot. Cook for 2-3 minutes. Stir in the crushed tomatoes, tomato sauce, ketchup, worcestershire sauce, red wine vinegar, sugar, chili powder, ground mustard, smoked paprika, and cumin. Stir in the cooked lentils. Season with salt and black pepper, to taste. Cook on low for 10 minutes. Taste and adjust seasonings to your liking.
Serve the sloppy joe mixture on buns. You can also serve the sloppy joe mixture over spaghetti squash, quinoa, or make lettuce wraps.
Note-for vegan and gluten free-make sure you choose a worcestershire sauce that is vegan and gluten-free! The sloppy joe mixture will keep in the refrigerator for up to 3 days. You can also freeze it for up to 1 month. You might have to add a little liquid to the mixture when you reheat it.