In the bowl of a stand mixer, combine the whole wheat flour, bread flour, and salt.
In a separate bowl, mix lukewarm water, sugar, and yeast. Let sit for 5 minutes until bubbly.
In a small bowl, soak the cereal grains by adding 3 tablespoon of hot water to ¼ cup of multi-grain cereal. Let this sit for 5-10 minutes while you begin mixing the dough.
Once the yeast has activated and become bubbly, add the yeast mixture to the dry ingredients, along with the vegetable oil, and starter from the night before.
Knead the dough on low speed for about 3-5 minutes, or until all the dry ingredients are absorbed. Increase the speed to medium and mix the dough until it becomes smooth and elastic.
You can check to see if the dough is ready by taking a small piece of dough between your fingers and doing the "window pane" test. If it stretches into a thin membrane without tearing, then it's ready!
Add the soaked grains and oats and mix for 2-3 minutes to evenly distribute the grains.
Place the dough in a greased bowl, cover it with a clean towel, and let it rise in a warm place for about 1 hour, or until doubled in size.
Punch down the dough and shape it into 3 equal-size portions (about 260g each). Let the dough rest for about 10 minutes, then shape into baguettes. Place them in a baguette pan, or on a silicone-lined sheet pan. Brush the tops with a mixture of 1 tablespoon honey and 1 tablespoon warm water. Sprinkle each loaf with 1 teaspoon of rolled oats and 1 teaspoon of grains. Let them rise for another 25-30 minutes.
Preheat your oven to 375°F (190°C). Bake the bread for 25-30 minutes, or until golden brown and sounds hollow when tapped on the bottom.