Zest 1 teaspoon of the lemon rind and reserve. Cut the lemon in half.
Bring a medium saucepan of generously salted water to a boil. Add the farro and cook until just tender, 20 to 25 minutes. Drain and rinse under cold water, then set aside.
Meanwhile, heat 1 tablespoon of the olive oil in a skillet over medium heat. Season the salmon with salt and pepper. Add the salmon to the skillet and cook about 3 minutes per side, until just cooked through. Squeeze in the juice of one of the lemon halves. Set the salmon aside to cool slightly, then flake with a fork into chunks.
Squeeze the juice of the remaining lemon half into a small bowl, add the shallots, the reserved lemon zest and the remaining 2 tablespoons olive oil and whisk together. Season to taste with salt and pepper.
Divide the farro between 2 bowls. Arrange the salmon, radishes, peas and avocado over the farro and drizzle over the dressing. Garnish with dill and serve.