Cook pasta according to package directions. Drain well; set aside.
In heavy bottomed skillet, fry bacon over medium heat until well done and crisp. Remove from skillet to drain on paper towel. When cool enough to handle, crumble and set aside.
Drain all but 2 tablespoons bacon grease from skillet. Heat grease over medium heat; add shallots. Cook until soft and slightly caramelized, about 5 minutes. Whisk in flour, stirring constantly, until mixture is golden, about 2-3 minutes. Gradually add milk, stirring until smooth.
Increase heat to medium-high and bring sauce to boil; reduce heat and let simmer, stirring frequently, until smooth and thickened, about 10 minutes. Add shredded cheeses, stirring until melted. Add dry mustard and salt and pepper to taste.
Remove sauce from heat and stir in arugula and cooked noodles. Stir in all but handful tomatoes and bacon. Divide mac and cheese between 6-8 bowls. Garnish with reserved bacon and tomatoes; serve immediately.
To roast tomatoes, halve two pints cherry tomatoes and place cut- side- up on baking sheet lined with aluminum foil. Sprinkle with 1 tablespoon olive oil and a pinch salt. Roast at 250°F 2-3 hours.