If you don’t have fingerlings, sub in baby red or gold potatoes in their place. Look for freshly dug potatoes in farmer’s markets in the spring or late summer through early fall.
Put potatoes and salt in a medium saucepan and add enough water to cover by about 1 inch. Bring to a boil, stirring occasionally. Reduce heat and simmer, uncovered and stirring occasionally, until potatoes are easily pierced with a fork, about 20 minutes. Drain well; let cool until easy to handle, about 10 minutes. Transfer potatoes to a cutting board and coarsely chop. Let cool 5 minutes
Meanwhile, in a small skillet cook prosciutto in olive oil until crisp; drain and let cool. Combine mayo, yogurt, mustard, relish, and steak seasoning in a large bowl. Stir in peppers, celery, onion, and eggs.
Add potatoes and prosciutto to dressing mixture (reserve some for garnish, if you like); toss gently to coat. Chill at least 2 hours or up to 1 day. Toss, transfer to a serving dish (if you like), and sprinkle with paprika and reserved prosciutto (if using) before serving.