Cook pasta to packet instructions, save 1/2 cup pasta cooking water.
Place the cashews and sunflower seeds in a small bowl with boiling water to soak for about 5 minutes.
Heat a drizzle of olive oil in a saucepan over medium heat. Add the onion, garlic and capsicum and season with a pinch of salt. Sauté, stirring occasionally, for about 4 minutes until softened.
Add the onion, garlic, capsicum mixture to a high-speed blender along with the sun-dried tomatoes, harissa paste, nutritional yeast, tamari, almond milk, vinegar, maple syrup, and the soaked cashews and sunflower seeds. Blend until smooth and creamy. Season with salt to taste.
Add the sauce back into the pan you cooked the onions in, add in pasta water and pasta and stir until combined and glossy, cook together for a minute or so.
Serve with fresh dill/parsley/basil, several grinds of black pepper, and chilli flakes.