In a medium saucepan, heat the beans, stock, hot sauce and cumin over medium-low, stirring, until warm, about 10 minutes.
In a medium bowl, combine half the onion and jalapenos with the lemon juice and garlic. Season with salt; let stand 10 minutes. Mash in the avocados to make the guacamole.
In a small bowl, toss the remaining onion and jalapenos with the tomatoes and cilantro to make the salsa; season with salt.
Heat a large skillet over medium-high. Add one tortilla; cook until beginning to blister, about 1 minute per side. Repeat with remaining tortillas. Place one tortilla on a work surface. Spread one-quarter of the beans in a rectangle in the center, then top with one-quarter of the cheese, romaine, guacamole, salsa, sour cream and olives. Roll up, burrito- style. Repeat with the remaining tortillas and fillings. Cut burritos in half; divide among plates.