Prosciutto and Cheese Tartine

INGREDIENTS

1/2 cup

warm water (100° to 110°)

1 tsp

sugar

package dry yeast

5 3/5 oz

all-purpose flour (about 1 1/4 cups)

3 tbsp

olive oil, divided

5/8 tsp

kosher salt, divided

1/4 tsp

black pepper

Cooking spray

1/2 cup

coarsely chopped walnuts

1/3 cup

very thinly sliced red onion

1 tsp

chopped fresh thyme

2 cups

arugula

1 tsp

fresh lemon juice

2 oz

thinly sliced imported prosciutto

1 oz

fresh Parmigiano-Reggiano cheese, shaved