Lightly grease a 9 x 13-inch loaf pan with 2 teaspoons of the oil.
Combine the yeast, brown sugar, and water in a large mixing bowl. Stir with a wooden spoon to dissolve. Let stand for 5 minutes, or until the yeast looks creamy.
Add 3 1/2 cups of flour, the salt, and cocoa, stirring well to blend, adding more flour as needed to make a slightly sticky dough. Turn out onto a lightly floured surface. Knead until the dough comes together into a smooth, supple mass but is still slightly sticky, about 5 minutes.
Lightly oil a large mixing bowl with the remaining 1 teaspoon oil. Put the dough in the bowl and turn it to oil all sides. Cover with plastic wrap or a clean damp kitchen towel. Let stand in a warm, draft-free place until it doubles in size, about 1 1/2 hours.
Turn the dough out onto a lightly floured surface and pat into a rectangle about 1 inch thick. Fold one-third of the long end over toward the center, pressing down on the edge to seal. Fold the dough two more times toward the center, pressing and sealing both times, and pinching seams so they disappear into the dough. Roll the dough into a loaf shape and put in the greased loaf pan. Cover with plastic wrap and let rise until it doubles in size, about 30 minutes.
Preheat the oven to 400°F.
Remove the plastic. Bake until the bottom of the loaf makes a hollow sound when thumped with your fingers (take it out of the pan), about 30 minutes. Cool in the pan for 10 minutes, then turn out onto a wire rack and cool for at least 15 minutes before serving.
Yield; 1 loaf