Melt 3 tablespoons butter in a medium saucepan over medium-high heat. Once melted, add the onion and cook until softened, but not browned, about 7 to 10 minutes, stirring occasionally. Stir in the flour and cook 1 minute. Whisk in the milk, bay leaf, Old Bay Spice, Dijon mustard, Worcestershire sauce, and black pepper. Stirring frequently, bring up to a boil. Turn off the heat and whisk in the shredded cheddar. Remove and discard the bay leaf and stir in the noodles, tuna, peas, and cubed cheddar. Pour the tuna noodle mixture into the prepared dish.