In a small pan over medium heat, toast sunflower and pumpkin seeds until lightly colored and aromatic, about 5 minutes. Allow to cool.
Place the seeds in a food processor and pulse until the texture is crumbly. Set aside.
In a small pot over medium-high heat, add 1 tbsp. grapeseed oil, onion, and garlic. Sauté about 4 minutes until soft, stirring often, then add tomatoes. Cook until tomatoes are soft, about 5 minutes.
In a small pan, toast dried chiles until fragrant, then remove from heat, slice open, and discard the seeds. Add chiles to the pot with the softened tomatoes and cook a few more minutes until the chiles have softened.
Transfer the mixture to a blender and blend until very smooth.
Heat the remaining 2 tbsp. oil in a frying pan over medium heat, and add the seed mixture. Cook 4–5 minutes until golden brown, then add the blended sauce to the pan and fry, stirring occasionally, until it reaches a thick, chorizo-like consistency.
Bring a medium pot of water to a boil and add fingerling potatoes. Cook until tender, about 10 minutes. Slice the potatoes into 1⁄2-inch rounds, toss them into chorizo mixture, and reheat together.
Heat tortillas and transfer to a plate, stacking two for each taco. Spoon chorizo mixture on top and garnish with lime wedges. Serve with salsa.