To the bowl of a blender, add the full-fat coconut milk, peanut butter, lime juice, shallot, garlic, lemongrass, spices, coconut sugar, and salt. Blend on high speed until smooth, about 20 seconds. Taste and adjust saltiness and sweetness to your liking. At this point, you can add chili paste, or sriracha if you want to make it spicy.
Heat the oil in a large non-stick skillet over medium heat. Once hot, add the mushrooms and sautée for about 7 minutes, or until the mushrooms are tender. Pour in the sauce and let simmer for another 5 minutes.
Warm the taco shells or tortillas. Fill the tacos with the saucy mushrooms, adding more or less sauce to your liking. Top with fresh cilantro or basil, peanuts, and a drizzle of lime juice.