Mix vinegar, oil and chili flakes in a small bowl
Add seasoned meat to a lightly oiled pot (about 6 to 8 cups capacity), and brown for 4 to 6 minutes, flipping every 2 minutes or so
Add mirepoix and chard stems and cook for a couple of minutes
Add mushrooms and zucchini, and cook, covered, for 2 to 4 minutes, stirring occasionally.
Add 3 cups of water and bring to a boil, the reduce to a strong simmer.
Add chard and cook for another 4 to 6 minutes, until chard stems are softened and zucchini centers are just starting to slump
Serve with the chili oil mixture on top.