Add pumpkin seeds to a large Dutch oven or large heavy-bottomed pot over medium heat and toast, stirring occasionally, until toasty, fragrant and popping noises begin, about 4 minutes. Transfer seeds to a bowl.
Pat chicken thighs dry; season with 1 teaspoon salt and ½ teaspoon pepper. Heat Dutch oven over medium-high. Add chicken, skin-side down, and cook until golden brown, 6–8 minutes, flip and continue to cook until browned on second side, about 4 minutes.
Add tomatillos, onion, chiles, garlic, oregano, 1 teaspoon salt and broth to Dutch oven with chicken.
Bring to a boil over high heat, then reduce to a simmer, partially cover, and cook until chicken is cooked through and vegetables start to break down, 35–40 minutes.
Using tongs, transfer chicken to a plate; set aside to cool.
Meanwhile, set a fine mesh sieve over a large bowl and pour borth and liquids into strainer. Press on solids to extract excess liquid. Skim grease off broth.
Transfer solids to a blender, add toasted pepitas and ¾ cup roughly chopped cilantro leaves and tender stems; blend until smooth.
Remove and discard skin from chicken; shred chicken. Discard bones.
Add puréed mixture, reserved broth, and shredded chicken back to pot. Stir in hominy and 3 tablespoons lime juice; bring to a simmer and cook until hominy has slightly plumped and become tender; about 10 minutes. Season with salt and pepper to taste.
Divide between bowls and top with cilantro, diced avocado, shredded cabbage, and thinly sliced radishes.