Heat a large pot or dutch oven over medium heat with 1 tbsp. of oil (2 tbsp. for 4 servings). Once hot and shimmering, add mirepoix and cook for 4-5 minutes until softened.
While mirepoix is cooking, bring vinegar and sugar to a boil in a small saucepan. Once sugar has dissolved and the mixture is simmering, add red onion, toss to coat and cover with a lid. Remove from heat and set aside to allow onions to pickle.
Once the vegetables are softened, add the garlic and chili powder and increase heat to medium-high. Cook for 1 minute, then add the fire roasted tomatoes and 1 cup of water (2 cups for 4 servings). Drain and rinse the lentils and kidney beans and add to the pot. Season with salt and pepper to taste. Bring chili to a boil, then reduce heat to medium and simmer for 15 minutes.
To prepare the avocado salsa, dice the avocado and place into a small bowl. Wash and finely tear or mince the cilantro, setting aside a few leaves for garnish if desired. Toss the avocado, cilantro and half of the lime juice with a pinch of salt. Slice the remaining lime into wedges.
To assemble your chili, divide between serving dishes and top with pickled red onion, avocado salsa, cheese and lime wedges. Sprinkle on red pepper flakes to add some heat if desired. Garnish with remaining cilantro. Enjoy!