In an effort to explain succinctly what the Gospel is:
It's the complete Story of God, and the consequent good news of his final, complete and atoning work for us. The Gospel is something done in eternity, satisfied in the future and available by faith in the present, to redeem us and bring us to God.
To the unchurched, I can't really fit it into a neat propositional statement, but would rather enthusiastically invite them to hear the Story (hear the Good News!) Short of that, I struggle but offer idioms like "Jesus loves you," which without the Story (and context) admittedly sounds shallow. So we tell them it's "Good news" and then labor to tell them what it is and what it means.
The Gospel is NOT, I repeat NOT (nor ever has been) steps or how-tos. It's good news! He did it! You can get in on this the same way Abraham did (
Gen 4). It's not bad news, and it won't leave you begging for a way in (trying to stammer in tongues). It's yours -- just believe. In fact, He is even working to help you believe! God elects. We respond by trusting that He is who He said He is, making our place in His story.