In a small bowl, combine the 60g rolled oats for the smoothie with the 240ml cold milk, then let sit for 10 minutes to soften. Soaking helps the oats blend fully and gives the smoothie a creamy, muffin-like texture instead of a gritty raw-oat one. That ten-minute window gives the oats' own starches real time to absorb the milk and soften from the inside, leaving the blades with something genuinely pliable to work through.

In a small bowl, mix the rolled oats, flour, brown sugar, cinnamon, and salt, then add the melted butter and toss until you have small moist crumbs. Cook the crumbs in a small dry or lightly buttered skillet over low to medium-low heat, stirring often, for 5–8 minutes, until golden and lightly crisp, or alternatively bake at 175°C / 350°F for about 8–10 minutes. Transfer to a plate and cool completely. Do not let the crumbs darken too far — they should be golden, dry, and lightly crisp, not bitter or deeply browned. That line between golden and overdone matters directly to flavour here, since sugar and butter both turn bitter past a certain point of browning, and there's no way to walk that back once it happens.

To a blender, add the soaked oats and milk, Greek yogurt, bananas, maple syrup or honey, vanilla, cinnamon, salt, lemon zest, lemon juice, and frozen blueberries. Blend until very smooth and thick, stopping once or twice to scrape down the sides if needed. Add the frozen blueberries last so the blades can pull everything down more efficiently and the smoothie stays cold and thick. That order matters because blending the softer, already-liquid ingredients first gives the blades real momentum before they ever have to work through a dense pile of frozen fruit.

Check the consistency — the smoothie should be thick, creamy, and breakfast-like, not thin. If it's too thick to pour, add more milk, 1–2 tablespoons at a time; if it's too thin, add a few more frozen blueberries or a little extra yogurt. Taste and adjust sweetness if needed. The finished smoothie should taste clearly of blueberry first, then vanilla-oat "muffin" notes, with the lemon only lifting the fruit flavour in the background. That order of flavours is exactly what separates this from a plain blueberry smoothie, since the oat and vanilla notes are what give it genuine muffin character rather than simply fruit and dairy.

Pour into 4 glasses, about 250ml each. Top each serving with 3 fresh blueberries, a light sprinkle of rolled oats, and a spoonful or pinch of the golden crumb topping, then serve immediately. That immediate serving protects the crumb topping specifically, since it softens fairly quickly once it meets the smoothie's surface, losing the crisp contrast it was cooked to provide.