Soak your cashews overnight or for at least a few hours to soften their texture. When they’re ready, roast the poblanos until the skins are blackened, making sure to turn them a couple of times throughout. Transfer the poblanos to a bag or bowl with plastic wrap over top to help loosen the skins. Once they have steamed, peel the skins off, cut them open, and remove the seeds and veins.
In the meantime, heat some olive oil in a skillet over medium-low. Sauté the onions for a few minutes, then add in the garlic and cook until fragrant.
Add the cooked vegetables, drained cashews, plant milk, cilantro, lemon juice, and salt to a blender. Mix everything on high until the sauce is smooth and creamy. Taste and adjust the seasonings as needed. If the sauce feels too thick, thin it out with pasta water for a better consistency.
Cook the pasta in a pot of salted water until al dente (for reference, ours takes 12 minutes). Save about a half cup of the cooking water, then drain the pasta and toss it with a little olive oil.
Toss the cooked spaghetti in the green sauce until everything is well-coated, then serve it immediately with your favorite garnishes. Happy eating!