Heat 1 tablespoon of oil in a saucepan over low- medium heat, roast the cashews stirring continuously until they are light golden brown. It will take about 2 minutes.
Turn off the heat and take out the cashews over a paper towel.
Use the same saucepan and add the remaining oil, heat the oil over medium heat until it is moderately hot. Add the mustard seeds as seeds crack add curry leaves and green chili, stir-fry for few seconds. Be careful curry leaves splatter.
Add carrots, green beans, corn, turmeric, and salt stir-fry for 3 minutes over medium heat. Add vermicelli and gently mix them with vegetables, add water. Bring it to boil over high-medium heat.
As vegetables come to boil reduce the heat to low and cover the pan. Let it cook till all the water has evaporated. Stir in between once, it will take about 10 minutes. Vermicelli should be moist.
Gently stir in the lemon juice, garnish with roasted cashews.
Serve hot.