Preheat the oven to 400ºF. Line a large baking sheet with parchment paper.
Cut 1 inch off the edges of the cornbread, then cut the edges into 1 inch cubes. Repeat with as much of the inside of the cornbread as you desire for croutons, and arrange the cut pieces in an even layer on the baking sheet. Spray or brush lightly with olive oil and bake, tossing once, until lightly browned and beginning to crisp, 10-15 minutes.
Meanwhile, heat a large skillet over medium heat. Add the chickpeas and ¾ cup barbecue sauce and stir until coated. Allow to simmer 5-10 minutes, stirring frequently, until the sauce has thickened and the chickpeas are hot. Remove from the heat and add another spoonful or two of sauce if you desire.
To assemble the salads, layer arugula, tomatoes, onions, chickpeas, croutons, and microgreens (if using) amongst 4-6 plates. Drizzle with additional barbecue sauce and enjoy.