Place pinto beans in a large stock pot with enough water to cover; soak 8 hours to overnight. Drain.
Cover beans with about 3 inches water in the same stock pot; cook over medium-low heat until tender, 35 to 40 minutes. Drain.
Heat ¼ cup vegetable oil in a skillet over medium-high heat. Add pumpkin seeds; cook and stir until light brown and popping, about 6 minutes. Cool slightly, about 5 minutes.
Transfer pumpkin seeds and oil to a blender or the bowl of a food processor; blend until smooth. Add half each tomatillos, arugula, serranos, spinach, lettuce, parsley, and cilantro to the blender; blend until smooth. Pour into a large bowl. Repeat with remaining half each tomatillos, arugula, serranos, spinach, lettuce, parsley, and cilantro.
Heat remaining ¼ cup oil in a deep pot; carefully add tomatillo sauce. Simmer, stirring with a wooden spoon, until thickened, about 30 minutes.
Add pinto beans, vegetable stock, and hominy to the pot; bring to a boil. Reduce heat to low; simmer, uncovered, until flavors are thoroughly blended, about 15 minutes. Season with salt and black pepper.
