Within hours, Mr Cheema was dead and Miss Choongh was fighting for her life after being poisoned with Indian aconite - known as the Queen of Poisons.
After her arrest Singh, a mother of three, tried to blame her brother-in-law Varinder for the death.
But a lodger at the house saw her take a container with the curry out of the fridge earlier in the day, the court heard.
Edward Brown, QC, prosecuting, said: "Perhaps jealousy, anger and revenge all playing their part, Lakhvir Singh decided to poison them using an extremely toxic and deadly poison, possibly brought especially from India."
The court heard that after the engagement became final in November 2008, Singh went to India and returned three weeks later. Another week later, Mr Cheema was taken to hospital.
Mr Cheema, known as "Lucky", was discharged after a week but doctors were unable to say what had caused his illness.
The judge gave the jury, which had been considering its verdicts for four days, a majority direction in respect of a charge, that Singh administered poison to Mr Cheema in December 2008.
The jury will resume its deliberations on Thursday and sentencing will take place after the jury returns its final verdict.
Miss Choongh gave evidence in the trial detailing how the couple fell ill while discussing their wedding plans.
"Lucky said to me 'I am not feeling very well. My face has become numb and when I touch it, I cannot feel it'."
Ms Choongh had a shower and then said she began feeling similar symptoms.
Gurjeet Choongh was in a coma for two days
"He said that everything seemed to be going dark. He could not see anything and was losing feelings in his body," Ms Choongh said.
"He was touching his tongue and could not feel anything. He was having to support himself. He said 'I think this problem is because of the food we have eaten'.
"I was feeling the same. Everything was going dark. I began to feel dizzy. It was difficult to stand up. My tummy was hurting."
Suspicious that Singh had poisoned them, Mr Cheema rang for an ambulance.
He told the operator: "Someone put poison in our food... she is my ex-girlfriend."
He died within an hour of arriving at the West Middlesex Hospital.
The last thing Ms Choongh remembers is sitting on a hospital bed before being placed in a coma for two days while doctors traced the poison and gave her an antidote.
Police later found traces of the poison among herbs in Singh's coat pocket and in her handbag.
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