Heat the oil and garlic in a stainless skillet over medium heat until the garlic begins to become fragrant, about 1 minute. Add the shallots and beans and stir often until they are nicely browned, about 5 minutes (if they get dark too quickly, reduce the heat to medium-low).
Stir in the thyme, red pepper flakes, salt and then the lemon juice and cook until the beans are tender, 3 to 5 minutes. Stir in the arugula leaves, cooking until they are just wilted, about another 2 minutes. Serve hot, at room temperature, or cold.