Remove the perch fillets from the packaging and place in a colander over a deep bowl to catch the liquid.
Cover the colander with a damp towel or food-safe plastic wrap and place in the refrigerator. The fillets are thawed when they have reached a certain degree of elasticity.
Blanch the beet greens and chard in boiling water for 5 minutes.
In a large pot, sauté the onion; once wilted, add the chard, beet greens and celery and continue to sauté.
Once the liquid has evaporated, quench with wine and add the tomato paste.
As soon as the ingredients start to boil, add the perch fillets.
Stir gently and let cook on a medium heat for 15-20 minutes.
Just before the end of the cooking time, add the lemon juice and season with salt and pepper.
Best served with potatoes.
The dish would be just as delicious if you used spinach instead of chard.