Take 4-5 cups water in a deep saucepan, bring it to boil over medium flame. When it start boiling, add 3/4 cup Penne pasta and 1/2 teaspoon salt.

Boil them until al-dente (cooked but not very soft). It will take around 10-12 minutes.

Transfer cooked pasta to a large colander and drain excess water.
While pasta is cooking, heat 1/2 teaspoon oil in a pan or kadhai over high flame. Add 1/4 cup chopped carrot, 1/4 cup chopped green capsicum, 1/4 cup chopped red capsicum, 1/4 cup chopped broccoli and salt.

Stir and cook until veggies are little cooked but still crunchy, for around 2-3 minutes. Turn off the flame and transfer them to a plate.

Add 1½ tablespoons maida (all-purpose flour). Stir continuously and cook for a minute.

Pour 1½ cups milk little by little while stirring continuously with a whisk. Stir and mix for 1-2 minutes.

Reduce flame to low. Continue stirring and cooking until mixture starts to thicken. It will take around 3-4 minutes depending on the size and thickness of the pan. When mixture starts to coat the back of a spoon as shown in the picture here, it means that it has started to thicken.
Add sautéd vegetables and pasta. Add 1/4 teaspoon oregano, 1/4 teaspoon red chilli flakes, a pinch of black pepper powder and salt.

Turn off the flame. Mix well.