Make the dressing. Combine the yogurt, lemon juice, olive oil, and salt in a measuring cup or small bowl. Whisk with a fork until creamy and emulsified. Taste and adjust the seasoning as needed.
Preheat the oven to 375° F. Line a rimmed sheet pan with parchment, nonstick foil, or a silicone baking mat. Add the bread pieces and both seeds. Drizzle with the oil, 1 pinch of salt, and the pepper. Toss with your hands until everything is coated and seasoned. Bake for about 16 minutes, until the bread is toasty and the seeds are colorful. Let cool completely.
Meanwhile, combine the cucumbers, radishes, onion, and remaining pinch of salt in a large bowl. Toss with your hands. Top with half the herbs.
When the bread and seeds are totally cool, add all the bread to the bowl, plus some of the seeds and 1 avocado. Add the dressing and toss until everything is coated. Season with salt to taste. Let hang out for a few minutes while you go find a big serving platter.
Dump the avocado panzanella onto the platter and spread out. Drizzle with olive oil. Top evenly with the remaining avocado, herbs, and seeds.
Emma is the food editor at Food52. Before this, she worked a lot of odd jobs, all at the same time. Think: stir-frying noodles "on the fly," baking dozens of pastries at 3 a.m., reviewing restaurants, and writing articles about everything from how to use leftover mashed potatoes to the history of pies in North Carolina. Now she lives in Maplewood, New Jersey with her husband and their cat, Butter. Stay tuned every Tuesday for Emma's cooking column, Big Little Recipes, all about big flavor and little ingredient lists. And see what she's up to on Instagram at @emmalaperruque.