Cook Pasta: Cook tagliatelle according to package directions, minus 1 minute.
Prep Vegetables: Thinly slice courgette, red onion, garlic, and mint.
Sauté Aromatics: Sauté onion and garlic in olive oil until softened.
Add Peas and Courgette: Stir in peas and courgette, cooking briefly.
Create Sauce: Deglaze pan with pasta water, then stir in nutritional yeast and miso. Add more pasta water if needed for desired consistency.
Season: Stir in most of the mint and lemon zest.
Combine: Drain pasta, reserving some water. Add pasta to skillet and toss to coat.
Finish: Add lemon juice, toss again and serve immediately. Garnish with mint and drizzle the remaining olive oil on top.