Preheat broiler to high. Arrange tomatillos, poblano, jalapeño, and onion cut-side-down on a foil-lined baking sheet. Broil 5 to 7 minutes until charred and blistered.
Heat a dry skillet over medium heat. Add pepitas and stir constantly for 3 to 4 minutes until golden and lightly popping. Remove and set aside.
Add charred vegetables, garlic, toasted pepitas, cilantro, oregano, and ½ cup broth to a blender. Blend until completely smooth. Season with salt.
Heat olive oil in a Dutch oven over medium-high heat. Pour in the blended sauce and cook 8 to 10 minutes, stirring frequently, until slightly darkened and reduced.
Add remaining broth, hominy, and shredded chicken. Stir and bring to a gentle boil. Reduce heat and simmer uncovered for 20 to 25 minutes. Adjust seasoning.
Ladle into bowls and top with cabbage, radishes, avocado, cilantro, lime juice, oregano, and crushed tostadas. Serve hot.
