Toss the coleslaw mix with a portion of the jalapeño brine in a bowl and season with salt and pepper to taste. In a separate bowl, whisk the sour cream and a portion of the lime juice together until smooth.

Adjust the oven racks to the upper-middle and lower-middle positions and heat the oven to 450°F. Combine the refried beans, minced jalapeños, and the remaining jalapeño brine in a bowl, seasoning with salt and pepper to taste.

Spread the bean mixture evenly over the tostadas and arrange them on two rimmed baking sheets. Bake until the beans are warmed through, 5 to 10 minutes.

Heat the oil in a large skillet over medium-high heat until just smoking. Add the onions and peppers and cook until softened and lightly browned, 5 to 7 minutes.

Stir in the garlic and cook until fragrant. Remove from the heat, stir in the remaining lime juice, and season with salt and pepper to taste.

Top the warm tostadas with the sautéed vegetables, the dressed slaw, and the crumbled queso fresco. Drizzle with the sour cream mixture, sprinkle with cilantro leaves, and serve immediately while the shells are still crisp.