Cook and mash lentils: Simmer ½ cup dried lentils in water for ~20 minutes until soft. Drain and mash.
Activate the yeast: Warm ½ cup water to 105–110°F, stir in yeast, and let foam 5–10 minutes.
Mix dry ingredients: Combine flours and salt in a large bowl.
Combine wet and dry: Add mashed lentils and yeast mixture, plus 1 cup water, mixing until a rough dough forms. Add remaining water as needed.
Knead dough: Knead 8–10 minutes until cohesive and slightly tacky.
First rise: Place in an oiled bowl, cover, and let rise 1 hour.
Shape and score: Form into a round loaf. Score with concentric circles or your favorite pattern. Brush lightly with olive oil.
Bake: 450°F for 40 minutes until golden brown and hollow-sounding, or 205°F internal temperature.
Cool and enjoy: Rest at least 30–60 minutes before slicing.