London Rocket (Sisymbrium irio L.) as Healthy Green: Bioactive Compounds and Bioactivity of Plants Grown in Wild and Controlled Environments

London rocket (Sisymbrium irio) is a wild green consumed globally, yet its phytochemical composition remains underexplored. In this study, we analyzed the leaves of wild S. irio plants and those grown in controlled environments (GCE) with varying electrical conductivities (EC) and light spectra. Plants were assessed for growth, phenolic content, vitamin C, antioxidant activity, glucosinolates, and antiproliferative effects against HT-29 human colorectal cancer cells. The optimal biomass yield occurred at the EC levels of 3.0–3.5 dS m−1 under Valoya® LED light. Wild plants showed higher antioxidant activity (DPPH and ABTS assays) than GCE samples, with values of 8.03–8.67 and 6.49–6.81 mmol TE per 100 g dry weight, respectively. The vitamin C range was 50.7–84.3 and 84.5–186.9 mg 100 g−1 fresh weight for GCE and wild samples, respectively. Phenolic content was higher in wild plants than in the GCE ones, with apigetrin as the primary phenolic compound. The MTT assay showed that ethanol extracts from wild plants weakly inhibited HT-29 cell growth, with a GI50 of 210–380 µg mL−1 after 72 h of cells exposure to plant extracts. Principal Component Analysis suggested that EC and UV exposure increase the antioxidant activity, total phenolics, and glucosinolates in wild plants, offering insights into the bioactive profiles of S. irio leaves.