Preheat oven to 325 degrees F. Grease a 9 x 13 inch baking dish, set aside.
Brown the ground beef until just cooked through over medium-high heat, drain fat. Add taco seasoning and 3/4 cup of water, bring to a boil, then reduce heat and simmer, uncovered, for 3-4 minutes or until reduced.
Meanwhile, in a medium bowl, mix sour cream, mayo, half of the cheese, and half of the onion together and set aside.
Heat green pepper, onion, and jalapenos in a skillet until onions are translucent, about 5 minutes. Remove from heat.
In a large bowl, add bisquick and 1 cup water. Mix well to form a soft dough. Spread into prepared pan, press it up the sides of the dish about a half inch high on all sides.
On top of the biscuit dough, layer the remaining ingredients in even layers, in the following order: ground beef, diced tomatoes, green peppers mixture, sour cream mixture, and then top it all off with the remaining cheddar cheese.
Bake on the middle rack for 30-35 minutes or until heated through and cheese is melted. Let set for 5 minutes before cutting into slices and serving.