Toast and soften the chiles: Heat a dry skillet or comal over medium heat. Toast 2 dried guajillo chiles and 2-4 dried chiles de árbol for 1–2 minutes until fragrant. Transfer to a small pot of simmering water. Remove the pot from the heat and let soak until soft, about 15 minutes.
Char the vegetables: In the same skillet or comal over medium-high heat, add the Roma tomato, 1/2 white onion, and 2 peeled garlic cloves. Sear for 5–7 minutes until lightly charred on all sides. Watch the garlic and remove it as soon as it is lightly charred. If it burns it will be bitter.
Blend the diabla sauce: Transfer the charred vegetables and drained chiles to a blender with the 1/2 teaspoon dried oregano, 1/2 teaspoon ground cumin, and 1/2 teaspoon kosher salt. Blend until smooth and strain if you prefer a silkier spicy red sauce.
Sear the shrimp: Pat 1 pound large shrimp dry with paper towels and season with 1/2 teaspoon garlic powder and a pinch of salt. Heat 1 tablespoon olive oil in a large skillet over medium-high heat. Cook the shrimp for 1–2 minutes per side until starting to turn pink.
Simmer in the sauce: Pour the diabla sauce over the shrimp. Reduce to medium-low heat and simmer for 2–3 minutes, stirring frequently, until the sauce thickens and the shrimp are cooked through.
Serve: Garnish with fresh cilantro and lime wedges. Serve immediately with Mexican white rice and warm corn tortillas.
