In the bowl of a stand mixer, combine warm water, sourdough discard, and yeast. Let sit for 5 minutes to activate.
Add salt and gradually mix in flour. Knead on medium speed for 5–10 minutes, until dough is smooth. (Adding extra flour 1 tbsp at a time if bread is still to wet).
Transfer to a large bowl, cover with plastic wrap or a damp towel, and let dough rise in a warm place until doubled (about 2 hours).
Coat a cast iron skillet or baking dish with avocado oil. Press dough evenly into the pan.
Oil your fingers and dimple the top of the dough. Drizzle with more oil.
Cover and let the dough rise again for 1–2 hours until puffy.
Mix cinnamon and sugar in a small bowl. Sprinkle over dough, then drizzle with melted butter.
Bake in a 400°F oven for 30–35 minutes, or until golden brown.
Whisk glaze ingredients together in a small bowl and drizzle over warm focaccia before serving.