Heat a large pot of water to boil for pasta.
Place saffron in small bowl and cover with boiling water to steep and bloom.
Salt water and drop spaghetti, undercook by 1 minute.
Meanwhile, heat a large skillet over medium-high heat with EVOO, 2 turns of the pan, about 2 tablespoons. Sauté the asparagus, peas, zucchini, onions and fava 3-4 minutes, add garlic, season with salt and pepper and stir a minute or 2 more, then turn off heat.
Place the herbs, chilies, zest and juice of 1 lemon, about ¼ cup EVOO, salt and pepper in a food processor and pulse into a pesto-like herb sauce.
Toss drained pasta with saffron and its water, herb sauce and butter, adjust seasonings and top with grated or shredded cheese.