This soup can be cooked on the stove, in an Instant Pot or in a Thermomix. I usually make it in the Instant Pot because I can set the timer then leave it to cook, and when I come back(or get home if Ive been out), the soup is ready to eat.
Here is a link to the Instant Pot that I use (I have and recommend the 8 litre): Instant Pot 8 litre on Amazon (This is an affiliate link).

Ingredients
Serves 6-8
2 brown onions
3 sticks celery
3 carrots
2 zucchini (400-500g)
2 heaped tablespoons stock powder (I use Massel brand)
1 cup split red lentils
400g can chopped tomatoes
400g can condensed tomato soup (or use another can of chopped tomatoes)
3 tsp dried mixed herbs
7 cups boiling water
Salt and pepper to taste
Stove Top Method
Place onion into a food processor and pulse until finely chopped, but not pureed. Place into a large soup pot.
Add carrot and celery to food processor and chop finely. Place into pot.
Place zucchini into food processor and pulse until finely chopped; place in pot.
Add remaining ingredients to soup pot.
Bring to a boil and simmer until red lentils are very soft, about 20-25 minutes, stirring regularly.
Add salt and pepper to taste.
Pressure Cooker Method
Place onion into a food processor and pulse until finely chopped, but not pureed. Place into pressure cooker.
Add carrot and celery to food processor and chop finely. Place into pressure cooker.
Place zucchini into food processor and pulse until finely chopped; place in pressure cooker.
Add remaining ingredients to pressure cooker.
Cook at high pressure for 8 minutes. Allow pressure to drop naturally for 15 minutes then release remaining pressure.
Add salt and pepper to taste.
Thermomix Instructions
You will need to use the smaller quantities below to cook this soup in the Thermomix. (You can choose to use either condensed tomato soup or a tin of chopped tomatoes. It will work with either.)
Serves 4
1 brown onion
2 sticks celery
2 carrots
1 zucchini (250g)
1 tablespoon stock powder (I use Massel brand)
½ cup split red lentils
400g can chopped tomatoes OR 400g can condensed tomato soup
2 tsp dried mixed herbs
3 cups water (or enough to fill to maximum mark)
Salt and pepper to taste
Thermomix Method
Place onion, carrot and celery into Thermomix bowl. Chop 3 seconds/speed 5. Scrape down bowl.
Add zucchini. Chop 5 seconds/speed 5. Scrape down bowl.
Add tomatoes, lentils, stock and dried herbs. Add water to reach 2L (max) mark inside the bowl.
Cook 30 minutes/100C/reverse speed 2.5/MC on.
Add salt and pepper to taste.