Cook the pasta until al dente, according to package instructions.
While the pasta cooks, heat the olive oil over medium heat in a large pan. Sauté the garlic until fragrant and golden, about 1-2 minutes.
Add the green peas and cook for another 2 minutes.
Pour in a splash of white wine to deglaze the pan, simmering for 1 minute to reduce.
Stir in the oat cream, thyme, rosemary, and black pepper. Let the mixture simmer gently for a few minutes.
Add the spinach and cook until wilted, about 2-3 minutes.
Transfer the mixture to a tall cup and blend until smooth. Return the sauce to the pan.
Stir in the vegan butter and lemon juice. Season with salt.
Add the cooked pasta to the pan and toss to coat in the sauce. Adjust the consistency with reserved pasta water if needed.
Garnish with a few chopped walnuts and serve.