Smashed Chickpeas on Toast With Harissa Yogurt

Name: Smashed Chickpeas on Toast With Harissa Yogurt
Ingredients: 1 large shallot, finely chopped; 1 tsp. finely grated lemon zest; ¼ cup fresh lemon juice; 2 small garlic cloves, divided; 2 15.5-oz. cans chickpeas, rinsed; 2 celery stalks, finely chopped, plus tender celery heart leaves for serving; ½ cup chopped cilantro, plus sprigs for serving; 1 Tbsp. finely chopped peperoncini, plus more thinly sliced for serving; ¼ cup extra-virgin olive oil, plus more for drizzling; Kosher salt; 4 slices country-style bread, toasted; 1 cup plain whole-milk Greek yogurt; 4 tsp. harissa paste; Freshly ground black pepper