Lightly coat a 10 inch (25 cm) non stick skillet with margarine. Heat over medium heat. Place half of potato slices, in one layer, in hot skillet. Cover and cook 3 minutes or until potato slices are lightly brown. Turn potato slices over; cover and cook 3 more minutes or until lightly brown. Remove from skillet. Cook remaining potato slices. Remove from skillet. (Recipe can be prepared ahead of time up to this point.)
Overlap all cooked potato slices, in the bottom and up the sides of the skillet.
Sprinkle with basil. Whisk together eggs, milk and mustards in a large bowl. Season with salt and pepper. Pour over potato slices in skillet. Place tomato slices over egg mixture. Cover and cook over medium-low heat for 10 to 12 minutes or until eggs are set, lifting the edges to allow uncooked egg to run to bottom of skillet.
Cut into wedges to serve.