Preheat oven to 350°F. Line a rimmed baking sheet with parchment paper. Cut 6 of the tortillas in half crosswise; cut halves into 1/4-inch-wide strips. Place tortilla strips and 1 tablespoon of the oil in a small bowl; toss to coat. Spread in a single layer on prepared baking sheet. Bake in preheated oven until crispy and lightly browned, about 15 minutes. Sprinkle with 1/4 teaspoon of the salt. Set aside.

Stir together oregano and 1 teaspoon each of the cumin, ancho chile powder, and salt in a small bowl. Sprinkle mixture evenly over both sides of chicken thighs.

Select SAUTÉ setting on a programmable pressure multicooker (such as Instant Pot). (Times, instructions, and settings may vary according to cooker brand or model.) Select HIGH temperature setting, add remaining 2 tablespoons oil, and allow to preheat until oil is shimmering, 5 to 6 minutes. Add half of chicken, and cook until lightly browned, 2 to 3 minutes per side. Remove to a plate, and repeat with remaining chicken. Add onion, poblanos, bell pepper, and garlic to cooker, and cook, stirring often, until vegetables are slightly softened, about 5 minutes. Add tomato paste and remaining 1 teaspoon each salt, cumin, and chile powder; cook, stirring constantly, 1 minute. Stir in chicken stock, tomatoes, and chicken.4. Press CANCEL on multicooker. Cover cooker with lid, and lock in place. Turn steam release handle to SEALING position. Select MANUAL/PRESSURE COOK setting. Select HIGH pressure for 8 minutes. (It will take 10 to 15 minutes for cooker to come up to pressure before cooking begins.) When cooking has stopped, carefully turn steam release handle to VENTING position, and let steam fully escape (float valve will drop). (This will take 3 to 4 minutes.) Remove lid from cooker. Remove chicken from cooker, and shred with 2 forks; return meat to cooker. Chop remaining 4 corn tortillas. Add chopped tortillas and lime juice to cooker, and stir until tortillas begin to dissolve and slightly thicken broth. Top soup with crisp tortilla strips, cilantro, and avocado slices.