Place the spinach in a bowl, pour the salt and lemon juice over all - then toss until every leaf is covered. Set aside.
Heat the olive oil over medium high heat. Add the onion and stir until slightly browned, 4-6 minutes.
Add the rice and stir until every grain is coated with oil and the rice begins to crackle slightly about 4 minutes.
Add the garlic and mushrooms. Stir through.
Pour the wine over all, stirring constantly until it is completely absorbed.
Now the work begins: add the simmering vegetable broth a ladle at a time. Stir after each addition until the broth is completely absorbed. Continue in this way, not rushing, until the all the broth is incorporated into the rice - this will probably take about 20 minutes. The rice should be very slightly firm.
Add the spinach to the risotto and heat through - 2 or 3 minutes.