To a blender or food processor, add the basil, arugula, walnuts, juice from 1/2 of a lemon and garlic clove. Pulse until finely chopped. With the machine running, slowly add enough olive oil until it's fully incorporated and the texture is smooth. Salt the pesto to taste (I added about 1 teaspoon). Set aside.
To prepare the fava beans, pinch off the top of the pod and undo the seam, which will reveal the waxy fava beans. Remove the beans and repeat the shucking process until you've worked your way through all of the fava bean pods. Set a small pot of salted water over medium heat. When the water reaches a simmer, drop in the fava beans and cook for about 1 minute. Drain them and set 'em aside until they're cool enough to handle. Once they've cooled off a bit, pinch off their waxy outer layer, which will reveal a very bright green fava bean. Repeat with all of the fava beans.
Place a medium pot of salted water over high heat. Cook your pasta according to the package's directions, about 7-8 minutes. Drain the pasta, reserving about 1/2 cup of pasta water. Add the cooked pasta back to the empty pot and add the reserved pesto, goat cheese and a splash or two of pasta water; toss until the pasta is evenly coated, adding a bit more pasta water as needed. Salt to taste (I added a few more pinches of salt). Fold in the reserved fava beans and slices of prosciutto; give it a good toss and divide pasta amongst bowls.