In a large bowl, dissolve yeast and brown sugar in warm water. Let rest 5 minutes until foamy.
Mix salt into warm oatmeal. Add salted oatmeal and melted butter or oil to the proofed yeast. Blend well. Add dry oats. Add up to 5 cups flour until stiff dough forms. Rest 15 minutes.
Knead 10 minutes until dough is elastic and smooth. Add additional flour if needed, up to 1 cup.
Place dough in greased bowl. Let rise until doubled, about 1 hour.
Grease two 9x5" loaf pans.
In a small bowl, mix ⅔ cup packed brown sugar with 2 teaspoons cinnamon. In a separate small bowl, melt 2 Tablespoons butter. Set both aside.
Punch down dough. Separate into 2 portions.
Working with 1 dough portion at a time, on non-stick or lightly floured surface, roll out to 20" x 10" rectangle. Brush slightly more than half of the 2 Tablespoons melted butter to within 1" of the edge of the dough. Sprinkle slightly more than half of the cinnamon-sugar mixture over the melted butter.
Bring short edges on each side to meet in the middle, overlapping slightly.
Press gently to seal.
Spread remaining butter to within 1" of edge of new top of dough. Sprinkle with remaining cinnamon-sugar mixture.
Roll up dough starting with one of the short edges. Gently pinch edge to seal. Gently pinch ends of loaf to seal. Place seam-side down in greased pan.
Repeat with second portion of dough, remaining butter and remaining brown sugar and cinnamon.
Cover loaves with a tea towel and allow dough to rise until doubled, about 30 minutes. Preheat oven to 375°F.
Bake 375°F for 30-35 minutes. Carefully remove loaves from pans immediately. Allow to cool before slicing.