Heat 3 tablespoons coconut oil in a large skillet over medium-high heat until shimmering.
Add the cubed chicken breasts in a single layer and cook, turning every 2–3 minutes, until golden brown and cooked through, about 8–10 minutes total.
Meanwhile, in a medium bowl whisk together the juice and zest of 3 lemons, 1 1/2 cups vegetable broth, 1 tablespoon light soy sauce, 1 tablespoon cornstarch, and 4 tablespoons honey until smooth.
Pour the lemon sauce over the cooked chicken, reduce heat to low, then cover and cook until the sauce thickens, about 6–8 minutes.
Uncover, stir gently to coat the chicken, then sprinkle with 1/2 teaspoon poppy seeds and 1/4 cup diced green onions.
Serve warm.