Measure and organize all ingredients before beginning. Place the multigrain flour, granulated sugar, cinnamon, baking powder, and salt in a large mixing bowl. Whisk thoroughly so the cinnamon and leavening are distributed uniformly throughout the flour mixture and no concentrated pockets remain.
Freshly ground cinnamon may be used for a brighter and more pronounced spice flavor.
Add the finely grated carrot, shredded apple, drained crushed pineapple, dried fruit, sweetened coconut, sunflower seeds, pepitas, chia seeds, and hemp hearts to the dry mixture.
Stir until all additions are dispersed evenly. Pay particular attention to separating the carrot, apple, and pineapple throughout the flour mixture so that the ingredients do not collect in clumps. Some initial hydration of the dry ingredients from the moisture in the fruit and vegetables is normal.
In a separate bowl, whisk the room-temperature eggs with the vegetable oil and vanilla extract. Continue whisking for approximately 30 seconds, or until the mixture appears uniform, lightly creamy, and somewhat emulsified.
Using eggs at room temperature helps them combine more readily with the remaining ingredients.
Pour the egg-and-oil mixture into the bowl containing the dry ingredients and mix-ins.
Using a spatula, gently fold the mixtures together only until they are combined. Avoid excessive mixing, as additional agitation can develop the gluten and produce muffins with a tougher, denser texture.
The finished batter should remain slightly uneven and shaggy rather than completely smooth. A few small traces of dry flour are acceptable.
Preheat the oven to 350°F. Line 12–16 muffin cups with paper liners, or lightly coat the cups with a neutral-flavored oil.
Distribute the batter evenly among the prepared muffin cups, filling each approximately two-thirds to three-quarters full to provide sufficient space for rising.
Bake for 30–35 minutes. The muffins are ready when a toothpick inserted into the center comes out clean or carries only a few moist crumbs.
Allow the muffins to rest in the pan for 5 minutes, then remove them and transfer them to a wire cooling rack.