Bring a medium sauce pot of generously salted water to a boil. Add the elbow pasta and cook until just tender, 7 to 9 minutes. Drain and set aside.
While the water heats and the pasta cooks, make the chili.

• Rinse the white beans and kidney beans.

In a large frying pan over medium heat, warm 2 tablespoons oil until hot but not smoking. Stir in the mirepoix and chili spice blend, season with salt and pepper, and cook until fragrant, 1 to 2 minutes. Add the white beans, kidney beans, tomatoes, and vegetable broth and season with salt and pepper. Bring to a boil, reduce to a simmer, and cook, stirring occasionally, until the mirepoix is soft and the chili thickens, 7 to 9 minutes.
While the chili cooks, prepare the lime yogurt.

• Zest the lime.
• Juice the lime.

In a small bowl, stir together the yogurt, lime zest, and 1 tablespoon lime juice; season to taste with salt and pepper.

• Measure out ¼ cup cheddar for garnish.
• Trim the root ends from the scallions; thinly slice the scallions.
• Coarsely chop the cilantro.

Remove the chili from the heat. Stir in the elbow pasta and remaining ¾ cup cheddar. Season to taste with salt and pepper.

Transfer the mac ’n’ cheese to individual bowls. Set out the lime yogurt, remaining ¼ cup cheddar, scallions, and cilantro and invite everyone to add their own garnishes.