Keeley’s Across the Pond Grilled Cheese with Arugula and Caramelized Onions

1/2 lb Keeley’s Cheese Co. Across the Pond cheese, sliced 1/2 inch thin 1 medium yellow onion, sliced 1 Tbsp canola oil 1 large handful arugula, washed (substitute baby spinach if you’d like) 1/2 tsp extra-virgin olive oil 4 Tbsp butter, room temperature, divided…