Pre-heat the oven to 375°F.
Bake the bacon on a slotted pan to crisp, 12-14 minutes. Coarsely chop and reserve.
Separate the eggs, placing the yolks in one bowl and the whites in another. Whisk up the whites to medium-firm peaks. Whisk the yolks with the dry mustard, Herbes de Provence, garlic, salt, pepper, cheeses and bacon.
Heat a 10-inch skillet over medium to medium-high heat with the oil, one turn of the pan. When the oil is hot, add the leeks and lightly brown, 4-5 minutes; remove to a plate. Melt the butter in the skillet; let foam subside. Fold the egg whites into the yolks and pour the mixture into the skillet. Scatter the leeks and tomatoes over the eggs as they begin to set and the edges firm up. Transfer to the oven and bake for 15-18 minutes, until golden and puffed.