Caramelize the onions:

1. Melt the vegan butter in a saucepan over medium heat.
2. Add the sliced onions, salt, and sugar, and combine.
3. Lower the heat to medium-low and cook, occasionally stirring.
4. After 10 minutes, add the garlic and sage and stir.
5. Cook until the onions are deeply caramelized, about 30 minutes. If the onions begin to burn or stick, add a splash of water as necessary. Set aside to cool.

Prepare the dough:

1. Preheat the oven to 400˚F.
2. Add the flour, baking powder, garlic powder, and salt to a large bowl and mix.
3. Add the water and olive oil and mix until a shaggy dough forms.
4. Transfer the dough to a clean and floured work surface and knead until a smooth dough forms, about 2 minutes, adding sprinkles of flour as necessary.
5. Roll the dough out to a rectangle about ¼” thick. If the dough springs back and doesn’t want to roll out, cover with a damp towel and let it rest for 10 minutes.

Assemble & bake:

1. Transfer the rolled-out dough to a baking sheet. Use a fork to poke holes across the dough and drizzle or brush with olive oil. Bake for 10 minutes.
2. Remove the flatbread dough from the oven. If you want an extra golden crust, combine ¼ teaspoon of maple syrup with 1 tablespoon of non-dairy milk and brush it in a thin layer along the edges of the crust. Spread the vegan mozzarella and caramelized onions over the crust. Top with vegan parmesan.
3. Return to the oven and bake for another 17-20 minutes, until the cheese is melted and the crust is lightly golden.
4. Allow the flatbread to cool for at least 5 minutes. Top with arugula, a drizzle of olive oil, and black pepper. Slice and serve!