Preheat the oven to 350 degrees F (175 degrees C). Grease a loaf pan and line with parchment paper.
Combine flour, sugar, oats, ground chia seeds, and flaxseed meal in a large bowl; mix well.
Whisk eggs lightly in a separate bowl. Mix in orange juice and orange zest. Beat in butter and milk. Add egg mixture gradually to the flour mixture and whisk until well incorporated. Pour batter in the prepared loaf pan.
Bake in the preheated oven until a toothpick inserted into the center comes out clean, 40 to 50 minutes. Cool on a wire rack for 5 minutes. Run a table knife around the edges to loosen. Invert carefully onto a serving plate or cooling rack. Let cool completely.