Add the olive oil to a large pot over medium-high heat.
Once hot, add the onions, celery and carrots and cook until softened, about 5 minutes.
Add the turmeric, cumin, salt and pepper, stir and cook another minute until fragrant.
Add the broth to the pot, stir then add the lentils. Bring to a boil then reduce heat to low and simmer for about 20 minutes.
While stew cooks, make the pistou by combining all the ingredients except the olive oil in a food processor. Process until finely chopped. With the processor running, slowly drizzle in the olive oil until the mixture just comes together in a clumpy texture. Set aside.
Once lentils are tender, add the chard to the pot, stir and cook another 5 minutes until stems are softened and leaves are wilted. Season to taste with salt and pepper.
To serve, spoon grain of choice into serving bowl, ladle the stew on top and garnish with the pistou.