Heat oil in a skillet over medium heat; cook and stir onion until tender and browned, 15 to 20 minutes. Add ground beef and season with meat seasoning, garlic powder, herbes de Provence, salt, and pepper. Cook and stir until beef is browned and crumbly, about 5 minutes. Drain excess fat from skillet.
Beat eggs together in a bowl. Whisk in milk, mayonnaise, and flour; sprinkle with salt. Stir in beef mixture and 1 cup of Cheddar cheese. Pour into the pie shell.
Bake in preheated oven until a knife inserted into the center of quiche comes out clean, about 45 minutes. Sprinkle remaining cheese on top of the quiche. Allow to stand for 5 minutes before cutting.