Butter a 9" square baking pan and set aside. To make grits, cut onion in half. Reserve one half and finely chop the other half. Melt 2 tbsp. butter in a medium saucepan over low heat. Add the chopped onion and cook 5 minutes. Add the water and 3/4 tsp. salt; heat to boiling. Gradually whisk in grits, stirring constantly. Cook 5 - 7 minutes, stirring, until grits are very thick and cooked through. Spread grits evenly in the buttered pan and set aside to cool to room temperature.
Meanwhile, prepare greens: Chop remaining onion. In large skillet, cook bacon over medium heat until crisp. Add onion and red pepper flakes; cook 5 minutes. Stir in greens and remaining 1/4 tsp. salt. Cover and cook over medium-low heat 10 minutes, stirring occasionally. Uncover and cook 5 minutes longer to evaporate some of the liquid. Keep warm while finishing grits.
When grits have cooled completely, cut into 9 equal squares. Combine pecans and breadcrumbs in a wide shallow bowl. With a spatula, remove one square of grits. Turn over and brush the moist bottom side of the grits generously with egg. Sprinkle pecan mixture generously over this egg wash and pat down the mixture to seal pecan crust to the grits. Repeat with remaining grits squares, egg and pecan mixture.
Just before serving, melt 2 tbsp. butter in a large skillet over medium heat. In batches, place grits squares pecan crust-side down in butter and cook until browned and crisp about 5 – 8 minutes. Turn over and cook just to warm other side. Remove from skillet and keep warm. Brown remaining pecan crusts, adding another tablespoon or two of butter, if necessary.
To serve, arrange greens on a large platter and top with pecan-crusted grits. (Alternately, to serve a crowd, the grits squares can be cut in half diagonally to make 18 wedges.)