Roast both the bell peppers over an open flame till nicely charred all around. Cover with a cloth for a few minutes before peeling off the skin (this makes the process easier). Deseed the bell peppers and slice into thin strips. Alternatively, oven roast the bell peppers and then do the same.
Cut the mozzarella ball into wedges and keep aside.
In a bowl, add the sliced bell peppers, mustard dressing and watercress.
Heat olive oil in a pan and flash fry the sliced tomatoes for a few seconds, season with salt.
Cool slightly and add the tomatoes to the bell peppers along with the mozzarella wedges.
Season with salt and pepper, drizzle balsamic vinegar and toss lightly.
Serve immediately.