Heat the oil in a heavy large skillet over medium heat. Add the garlic and saute until fragrant, about 30 seconds. Stir in the sage and thyme. Add the tomatoes. Increase the heat to medium-high and simmer for 2 minutes. Add the beans. Simmer until the tomatoes are tender and the juices evaporate by half, about 5 minutes. Turn off heat and stir in the prosciutto, being careful not to overcook the prosciutto. Season the beans, to taste, with salt and pepper.
Arrange the arugula or mixed baby greens over a platter. Spoon the beans over the greens and serve.