Prep ingredients: Trim scallions, then thinly slice, keeping dark greens separate. Coarsely grate all of the cheddar on the large holes of a box grater. Squeeze 1 tablespoon lime juice into a medium bowl.

Cook aromatics: Heat 1 tablespoon oil in a medium skillet over medium-high. Add scallion whites and light greens and cook, stirring, until softened, about 2 minutes. Add 2¼ teaspoons taco seasoning and cook, stirring, about 30 seconds.

Add beans & corn: Add beans and their liquid. Bring to a simmer, and cook, stirring occasionally, until thickened and liquid is evaporated, about 4 minutes. Remove from heat and stir in corn and all but 2 tablespoons of the scallion dark greens (reserve rest for step 4). Season to taste with salt and pepper. Set aside to cool slightly.

Make pico de gallo: Chop tomatoes into ½-inch pieces. Peel and finely grate 1 large garlic clove. To the bowl with the lime juice, add tomatoes, garlic and reserved scallion dark greens. Season to taste with salt and pepper and stir to combine.

Fill chimichangas: Place 4 of the tortillas on a work surface (save rest for own use). Divide bean mixture evenly among tortillas and spread to a 5-inch square in the center of each. Top with cheese, then fold in sides of each tortilla and tightly roll up into a cylinder, like a burrito. Rinse and dry skillet. Heat ⅛ inch oil in same skillet over medium-high until shimmering.

Fry chimichangas & serve: Add chimichangas to oil, seam side down. Immediately reduce heat and fry over medium, turning occasionally, until browned all over, 5–7 minutes. If seam comes apart after turning, position rolls close enough so they help each other stay closed. Transfer, seam side down, to a paper towel. Halve chimichangas and serve with pico de gallo and sour cream.