Preheat your oven to 400°F and line two large baking sheets with parchment paper.
Dice the red bell pepper and zucchini into small pieces, and thinly slice the red onion.
Toss the vegetables on one baking sheet with olive oil, sea salt, and black pepper, then roast for 15 minutes until tender and slightly caramelized.
While vegetables roast, whisk the egg whites with dried oregano in a bowl until slightly frothy.
Pour the egg whites onto the second parchment-lined baking sheet, tilting the pan to ensure the liquid forms a thin, even rectangle.
Bake the egg white base for 10-12 minutes until the edges are crisp and the center is firm to the touch.
Remove the flatbread from the oven and evenly distribute the roasted vegetables, shredded chicken breast, and crumbled goat cheese over the top.
Return the flatbread to the oven for 3 minutes to melt the cheese and warm the toppings.
Garnish with fresh baby arugula, slice into squares, and serve immediately.