Wash and dry all produce. Preheat oven to 450 degrees. Cut potatoes into 1/2-inch cubes. Toss on a baking sheet with a large drizzle of olive oil. Season with salt and pepper. Roast in oven until golden brown, about 25 minutes total (we’ll be adding more ingredients to the sheet before the potatoes are done).

Halve, peel, and dice onion. Trim and discard woody bottom ends from asparagus, then cut stalks into 1-inch pieces, leaving tips whole. Zest lemon until you have 1 tsp zest, then cut into halves.

Heat a drizzle of olive oil in a large pan over medium-high heat. Add onion and cook, tossing, until golden brown, about 8 minutes. Season with salt and pepper. Add asparagus and cook, tossing, until tender, 3-4 minutes. Season with salt and pepper. Remove from heat.

Once potatoes are nearly crisp, after about 20 minutes of roasting, remove sheet from oven. Give potatoes a toss and push toward one side of sheet. Place 2 prosciutto slices on other side of sheet. Return sheet to oven and roast until potatoes and prosciutto are crisp, 5-7 minutes more. Remove prosciutto from sheet to cool.

Transfer potatoes to pan with hash. Add bread to same baking sheet and toast in oven until just crispy, 3-4 minutes. Once crisped prosciutto has cooled, roughly chop and add to same pan. Season with salt, pepper, and a squeeze of lemon.

In a small bowl, combine ricotta, lemon zest, and a squeeze of lemon. Season with pepper. Spread mixture on one side of each slice of bread. Tear remaining prosciutto into pieces and place on top. Cut each slice in half and divide between plates. Place a few pieces of asparagus from hash on top, then serve with remaining hash on side.