Place the chicken and potatoes into a large mixing bowl, then season with salt and pepper; set aside.
In a smaller mixing bowl, whisk together the mustard, Italian herbs, and 3 TBSP of olive oil. Once cohesive, drizzle the mixture over the chicken and potatoes. Toss to evenly coat. Set the bowl aside for 30 minutes leaving at a room temp. This will result in a more even cook.
Pop the zucchini into a large mixing bowl and drizzle it with the rest of the olive oil. Add the lemon zest and some salt and pepper; toss to coat.
Preheat the oven to 425º F.
Cover a sheet pan with parchment and transfer the chicken and potatoes to it, ensuring that the potatoes are evenly spread out/not sitting on top of one another.
Place the chicken and potatoes in the oven for 20 minutes. While these cook, you can whip up your yogurt sauce (see below).
After 20 minutes, lightly toss the potatoes and add the zucchini to the sheet pan, spreading the pieces out as evenly as possible.
Bake for another 20-25 minutes, or until the potatoes and chicken skin are golden and crisp. The chicken thighs should register an internal temperature of 160-165º F.
Drizzle the yogurt sauce over the sheet pan dinner or serve it on the side with lemon wedges and fresh herbs.