Prep your pan and oven. Heat the oven to 350°F (175°C). Line a 9x5-inch loaf pan with parchment and lightly oil the sides.
Mix dry ingredients. In a large bowl, whisk together oat flour, protein powder, baking powder, baking soda, salt, and ground flaxseed or chia.
Whisk wet ingredients. In another bowl, whisk eggs, Greek yogurt, 1/2 cup almond milk, oil, and honey/maple (if using) until smooth.
Combine and adjust. Stir the wet mixture into the dry. The batter should be thick but spoonable.
If it’s too stiff, add up to 1/4 cup more almond milk, 1 tablespoon at a time.
Pan and top. Transfer batter to the loaf pan, smooth the top, and sprinkle seeds if you like. Lightly press them in so they stick.
Bake. Bake 35–45 minutes, until the top is golden and a toothpick comes out mostly clean with a few moist crumbs. If it browns too fast, tent loosely with foil.
Cool completely. Let it cool in the pan for 10 minutes, then lift out and cool on a rack for at least 1 hour. Don’t slice while hot or it may crumble.
Slice and serve. Cut into 10–12 slices.
Great plain, toasted, or with a light spread of nut butter.