Preheat the broiler in your oven.
Place peppers, halved red onion, and garlic cloves on an aluminum foil-lined baking sheet. Lightly brush with olive oil.
Broil for 5-7 minutes in the top oven rack, turning occasionally until charred.
Transfer the roasted peppers to a plastic bag and let them steam for 10 minutes.
Peel off the charred skin, remove seeds, and chop the peppers.
In a blender, combine red onion, garlic, roasted poblanos, and cream. Blend until smooth and you have your Mexican crema!
Season with salt and pepper.
Cook spaghetti according to package instructions in a separate large pot.
Drain the cooked pasta and toss with creamy poblano sauce until evenly coated.
Plate the green spaghetti and top generously with crumbled feta cheese.
Garnish with freshly chopped parsley.