Measure out half each of onion flakes, cumin, chili powder, tomato powder, black bean flakes, corn, and bouillon cubes into 2 large resealable plastic bags.
Add 3 1/2 cups water to each bag and let sit about 10 minutes to rehydrate. Pour one bag at a time into a 2-qt. saucepan and heat over medium-high heat, stirring occasionally, until simmering, 12 to 15 minutes. Spoon into mugs and heat remaining soup.
Cut limes into wedges and avocado into cubes. Serve soup with tortilla chips, lime, and avocado.
*Find dried onion flakes with the spices at well-stocked grocery stores or online; find tomato powder online. Frontier Co-op black bean flakes rehydrate nicely for soup and chili ($1 1/1 lb.; frontiercoop.com). Harmony House Foods freeze-dried and dehydrated vegetables (such as carrots, green beans, and corn) taste great as snacks and in soups and stews (from $2.95/4 oz.; harmonyhousefoods.com).