Heat oil in a large pan. Add 1 cup onion and the garlic, and cook over low heat until translucent, about 2 minutes. Stir in beans, and cook for 3 minutes. Roughly mash with the back of a spoon, adding reserved liquid as needed to attain desired consistency.
Mix tomatoes with remaining 2 tablespoons onion and the salt. Mash avocados with jalapenos, 2 tablespoons sour cream, and the lemon juice.
Spread 1/2 inch mashed beans into bottom of each jar. Top with 2 tablespoons cheddar, 1 tablespoon scallions, cup tomato mixture, 3 tablespoons avocado mixture, 2 tablespoons sour cream, then 2 1/2 tablespoons olives. (Alternatively, layer all ingredients in a large bowl.) Serve with chips.